While the Disney properties in KH do retain their heteronormative romances (Belle/Beast, Ariel/Eric, the rest of princesses, Mickey/Minnie, etc), it's almost in stark contrast to what KH is willing to explore for OCs, which I'm fine with if it means Riku is never confirmed straight.
But yes, they better retain the same stance with the queer romances if brought into play. As much as I want to see a Strange World world (I'm one of two people here who saw it and liked it?), I don't know that Diazo is important enough to bring into the fold. For all its NPCs, even KHIII didn't seem to incorporate a lot of side characters. Diazo has less screentime than characters like Hans, Phil, Eeyore, and even Mochi, and they were treated with scant acknowledgement or even omitted all together. If he had been more prominent or had gone on the adventure with Ethan, then I might have more hope. Lightyear has a better chance if we focus on the first part of the film, which I don't think they would do.
We're seeing this representation emerge from Disney, but we're still not at the forefront. Disney themselves have mostly moved away from stories with romances and couples spearheading the main narrative. As far as WDAS goes, I've missed a few, but was the last one Tangled? I know Anna and Kristoff are a thing, but they feel secondary to Elsa's story or Elsa and Anna's story. We need a classic romance like Cinderella or Beauty and the Beast BUT GAY to really secure the possibility of the couple, the queerness being noticed when playing KH through that world.